1. Field of the Invention
This invention relates to semiconductor fabrication methods and apparatuses, and particularly to a method and an apparatus for stripping a photo-resist without causing damage to metal wirings of a substrate.
2. Description of the Prior Art
When an integrated circuit is fabricated on a semiconductor wafer, a polysilicon layer and a metal layer are patterned into conductive layers, and a contact hole and a via-hole are formed in insulating layers. Such small-scale patterning is usually achieved by using a lithography step. Photo-resist solution is first spread over the conductive/insulating layer, so that the conductive/insulating layer is covered by a photo-resist layer. A pattern image is optically transferred from a photo-mask to the photo-resist layer, thereby forming a latent image in the photo-resist layer. The latent image is then developed. Using the residual photo-resist as a mask, the conductive/insulating layer is patterned by way of a wet etching or a dry etching process. The photo-resist mask exposes a part of the conductive/insulating layer to etchant, and the etchant removes the part of the conductive/insulating layer. Upon completion of the wet/dry etching process, the residual photo-resist is stripped off.
Conventional methods for stripping the photo-resist include a dry stripping method and a wet stripping method.
The technology of the dry stripping method is called “ashing.” The photo-resist is exposed to oxygen plasma, so that the oxygen plasma ashes the photo-resist. However, the oxygen plasma is not effective against any reaction product that may exist. The reaction product remains on the inner surface of an inter-level insulating layer in particular. For this reason, ashing is not appropriate in a case where a reaction product is expected.
In the wet stripping method, various organic or inorganic solvents can be used to dissolve the photo-resist. The organic solvent can be acetone, n-methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO), or aminoethoxy ethanol. The inorganic solvent can contain sulfuric acid and hydrogen peroxide. The wet stripping method is less costly than the dry stripping method. However, the solvent and any reaction products that exist erode metal (aluminum) wires below the photo-resist after the photo-resist has been stripped off.
Referring to FIG. 3, a conventional wet stripping method for stripping a photo-resist includes the steps of: (a) wet cleaning a substrate using a wet stripping solvent; (b) rinsing the substrate using isopropyl alcohol (IPA); and (c) rinsing and neutralizing the substrate using a carbon dioxide (CO2) solution.
In step (a), a stripping solvent consisting of monoethanol amine and dimethyl sulfoxide ((CH3)2SO) is spread onto the substrate. After the photo-resist is stripped off, the solution operates to effect chemical change, as shown in the following chemical equation:C2H5O—NH2+3H2O→C2H5OH+NH4++3OH−Ammonia (NH4OH), a reaction product of the above chemical equation, intensively erodes the aluminum wires, as shown in the following chemical equation:6NH4++3OH−+Al→Al(OH)3+6NH3+3H2A speed of the erosion is approximately (0.167˜1.67)×10−10 m/s.
Accordingly, step (b) is performed to reduce or eliminate the aluminum erosion occurring in step (a). However, in practice, the isopropyl alcohol cannot effectively neutralize monoethanol amine, dimethyl sulfoxide or ammonia. The erosion of aluminum is not prevented.
Step (c) is an adjunct to the process of step (b). CO2 solution is used to neutralize the solution eroding the aluminum wires, as shown in the following chemical equation:2C2H5O—NH2+CO2→C2H5—NH3++C2H5O—NHCOO−above-described wet stripping method. The yield of the wet etching process is decreased accordingly. In addition, the need for the IPA rinsing step (b) and the CO2 solution rinsing step (b) necessarily adds to costs.
Referring FIG. 4, this represents a conventional apparatus for stripping a photo-resist as disclosed in Taiwan patent no. 490,072. The apparatus 10 includes a stripping vessel 20 filled with a stripping solvent, a rinsing vessel 30 filled with a rinsing solution, a drying device 40, a plurality of conveyors 50 mounted between the stripping vessel 20 and the rinsing vessel 30, and a control unit 60 for controlling the conveyors 50. However, the stripping solvent used to clean the substrate in the stripping vessel 20 consists of monoethanol amine and dimethyl sulfoxide. Thus the above-described aluminum erosion problem still occurs.
It is desired to provide a new method and apparatus for stripping a photo-resist that overcomes the above-described problems.